1. Field of the Invention
The present invention relates to a small brushless motor for recording-reproducing devices using, for example, disk media.
2. Description of the Related Art
In the conventional bearing housing structures for supporting the bearing member of a small brushless motor, a roughly central part of a stator base composed of a thin sheet of a ferrous metal material such as an iron sheet or a non-ferrous metal material such as aluminum was subjected to hole flanging and a bearing housing was formed integrally with the stator base from the same work as the stator base.
In such a bearing housing structure, the hole flange base portion had to be sealed by forming a bottom with a thrust-receiving member that supported the end of the rotary shaft of the motor on the side opposite to that of loading, held it so as to prevent a lubricating oil from leaking from the bearing, and was composed of a material other than the stator base.
The following is known about the conventional technology relating to the shape of the thrust-receiving member and methods for fixing such a member.
(1) The aforesaid receiving member is formed to have a plate-like shape and is secured with screws to the stator core via a flat part of a step portion provided on the periphery of the bearing housing of the stator base (for example, Japanese Patent Application Laid-open No. H9-103043).
(2) The aforesaid receiving member is formed by pressing or cutting as a cup-like metal ring member which is pressed in the hole flange base portion of the stator base (for example, Japanese Patent Application Laid-open No. H8-289523).
(3) The aforesaid receiving member is formed to have a disk-like shape and is fitted into a recess in the lower end portion of the bearing and caulked (for example, Japanese Patent Application Laid-open No. H8-275439).
(4) The aforesaid receiving member is formed to have a disk-like shape and is welded or adhesively bonded in the vicinity of the aforesaid opening so as to close the hole flange base portion of the stator base (for example, Japanese Patent Application Laid-open No. H8-214487).
However, the following problems are associated with the above-described conventional technology.
Namely, with the technology of (1), metal,chips are produced during tapping or during a screwing operation involving tapping and there is a risk of those metal chips penetrating into the bearing. Furthermore, the operability of threading and screwing is poor and there is a risk of the lubricating oil leaking from the seams.
With the technology of (2), there is a risk of the metal ring member falling out or detaching, a spread of dimensions in the thrust direction can easily occur, and the rotor can be brought into contact with the bearing portions, which will make the rotation thereof impossible.
With the technology of (3), because the end portion of the bearing is directly caulked, the inner diameter of the bearing can be changed, the caulked portion can become loose or detached, and the lubricating oil can leak out.
With the technology of (4), there is the danger of the workability of the welding and adhesion being poor, and of the welded portion and adhered portion peeling off or pin holes forming thereon, making the lubricating oil leak out.